This is due to a Major Upgrade of Hardware/API Software and many other components too much to list out.

OpenStreetMap API 0.6 is scheduled to go live on 17-19th April, 2009.

"Expect server downtime during that period. The current API will go into Read Only mode at 10:00am BST (9:00 UTC) Friday 17th April. You might need to upgrade your editor to use the new API after the work is complete. There may also be some hiccups in the following days."

Why so much downtime?

"Switching off" OSM for up to four days isn't something we take lightly, but we don't have much choice. We're moving the data from one database server to our shiny new one. Also there's a lot of processing to create changesets, fix utf8 bugs, deal with inconsistencies and stuff.

We will keep the API up and running in read-only mode for most of the weekend, and the website displaying maps, however we will need at least a short period of total downtime.

If you are a JOSM user, you will be able to download but not upload over much of the weekend, however you would be well advised to upload any mapping work before the weekend, and dont start any extensive editing work until you're up and running with API0.6 next week. Compatibility glitches are a possibility otherwise.

Mapperz hopes the upgrading goes smoothly and painlessly as possible. Good luck with the upgrade OSM team.Afterwards you will find OpenStreetMap at a faster pace for an even more enjoyable mapping experience.